Engaged: Amal Alamuddin has won the heart of Hollywood's most famous bachelor. Photo: Getty Images

The British law firm that employs Amal has also publicly offered its congratulations.

Doughty Street Chambers in London said on Monday it was ''delighted'' Alamuddin and the Oscar-winning heart-throb were to tie the knot.

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"The barristers and staff of Doughty Street Chambers offer their best wishes and congratulations to Ms Amal Alamuddin, a member of chambers, and Mr George Clooney on their engagement to be married,'' it said in a statement emailed to AFP news agency.

Alamuddin is a Lebanese-born British lawyer specialising in international law and human rights. Clooney has long shown interest in human rights issues such as the humanitarian crisis in Darfur.

Chief executive Robin Jackson said: ''Amal has been utterly wonderful since she arrived in chambers.

''She brings a bright light to everything she is involved in, and I am so delighted at her happy news.''

Alamuddin's clients have included former Ukrainian premier Yulia Tymoshenko, whose detention she challenged before the European Court of Human Rights, and WikiLeaks founder Julian Assange, during his extradition proceedings.

Leading rights lawyer Geoffrey Robertson, who worked with Amal on the Tymoshenko and Assange cases, said she was ''respected and admired'' by everyone at the firm.

''Amal Alamuddin is a brilliant and passionate defender of human rights who has put in the enormously hard work necessary to improving them,'' he said.

Alamuddin and Clooney were first seen in public as a couple in October and have since been seen on holiday in places including Tanzania and the Seychelles.

He was married to US actress Talia Balsam for four years between 1989 and 1993 but has shown little interest in settling down since, instead having a string of younger model and actress girlfriends over the years.